1. Field of the Invention
The present invention relates to a CMOS (complementary metal oxide semiconductor) image sensor, and more particularly to a CMOS image sensor adapted for an image pickup apparatus which can be installed in a cellular phone, a personal computer, or the like.
2. Description of Related Art
Recently, remarkable improvement of CPU performance, progress of image processing technology and the like have allowed to process digital image data easily. In particular, in the field of cellular phone or PDA (personal digital assistant), some types with a display which can display images appear on the market, and significant improvement of data transfer rate in radio communication may be expected in the near future. Accordingly, it is anticipated that transfer of image data between such types of cellular phones and PDAs are frequently carried out.
At present, after a subject image is converted to image data by a digital still camera or the like, transfer of such image data is carried out through internet by using a personal computer or the like. However, in order to transfer the image data in such a manner, both apparatuses, i.e., a digital still camera and a personal computer, are required. Lately, as an image input device of a mobile data terminal, a miniature camera module in which both an image pickup device and an optical lens system are mounted on a substrate, is proposed. Such a miniature camera module does not require to have a digital still camera nor a personal computer and enables picking up an image to send it to a person simply, by a cellular phone which can be carried around with ease.
Further, as an image pickup device for such a compact camera module, CMOS image sensors are given attention, in place of a conventional CCD sensor, for the following reason.
(1) CMOS image sensors can be fabricated by applying the present CMOS fabricating process for semiconductor devices such as photodiodes or the like, at low costs in comparison with CCD sensors.
(2) CMOS image sensors can be operated by a single power supply so that the power consumption for that can be restrained lower than that of CCD sensors.
(3) Signal processing circuits, e.g., a CMOS logic circuit, can be integrated in the sensor chip and therefore the CMOS image sensors can be miniaturized in comparison with CCD sensors.
However, in the case that the image pickup device and the optical lens system are mounted on a single substrate, the light receiving plane of the image pickup device has to be set at an in-focus position of the optical lens system optimally. Accordingly, adjustment for the purpose occurs a large problem. For example, when mounting the image pickup device and the optical lens system onto the same substrate, it is difficult to set the light receiving plane of the image pickup device at an in-focus position of the optical lens system optimally because of variation in thickness of the adhesive which is used for mounting the optical lens system onto the substrate and variation in size of the components. In order to improve the dimensional precision for setting the light receiving plane of the image pickup device at an in-focus position of the optical lens system, a high-precision setting technique or a separate mechanism for adjusting to obtain an in-focus state is required. Such a requirement increases the production costs.
Even when a CMOS image sensor is adopted instead of a CCD image sensor, the above-described problem arises similarly. Such a problem forms a large obstruction to producing a compact camera module at a low cost.
The present invention has been developed to resolve the above-described problem. An object of the invention is to provide a CMOS image sensor which is adapted for obtaining an image pickup device for a camera module and which can be produced at a low cost.
In accordance with one aspect of the invention, the CMOS image sensor comprising, a light receiving unit as a photoelectric converting device, and a signal processing circuit; further comprising:
a first layer comprising a color filter array and a microlens array layered thereon, which are provided on an upper surface of the light receiving unit; and
a second layer comprising at least one of a color filter and a microlens array, provided in a region of at least a portion of an upper surface of the signal processing circuit.
Herein, the term xe2x80x9cphotoelectric converting devicexe2x80x9d means xe2x80x9ca part comprising a plurality of pixels which are disposed in two-dimensions, each of the pixels having a photoelectric conversion elementxe2x80x9d. Each of the pixels generates a signal charge corresponding to the intensity of light received by each pixel. For example, each pixel of a general CMOS image sensor comprises a photodiode which performs photoelectric conversion and a CMOS transistor which performs charge amplification and switching.
The xe2x80x9csignal processing circuitxe2x80x9d means xe2x80x9ca circuit which comprises a driving circuit for driving the pixels in order, to obtain signal charges, an A/D converter for converting signal charges to digital signals, and a digital signal processing unit for forming image output signals by using the digital signalsxe2x80x9d.
The xe2x80x9ccolor filterxe2x80x9d means xe2x80x9ca filter which only allows light of specific color components to pass through. Typically, the color filter array provided on the light receiving unit comprises red, green and blue filters (primary color filters) or cyan, magenta and yellow filters (complementary color filters), which are arranged to correspond to pixels of the light receiving unit, respectively, to obtain color information. A color image can be obtained by composing the whole output signals from the pixels.
The xe2x80x9cmicrolens arrayxe2x80x9d means xe2x80x9ca plurality of microlenses, each having a hemisphere shape, arranged on the photoelectric converting device in two-dimensions, to increase the amount of light entering photodiodes as the photoelectric conversion elements of the pixels.
Next, the function and effects in the case of abutting a lens supporting member against the CMOS image sensor will explained as follows.
When a lens supporting member (including a lens frame) which supports an optical lens as a photographic optical system, is held by a substrate, while abutting portions (legs) of the lens supporting member are abutted against the upper surface of the CMOS image sensor, not positioned to a substrate, it is not required to consider variations in thickness of the adhesive between the substrate and the CMOS image sensor nor variations in height from the substrate to the light receiving plane of the CMOS image sensor, so that positioning in the direction of the optical axis can be performed precisely and assembly for an image pickup apparatus can be performed with little effort. In particular, 1-chip CMOS image sensor comprising a light receiving unit and a signal processing circuit which are integrated in the same semiconductor chip, can have the signal processing circuit with a large area enough to abut a lens supporting member against, in the outside of the light receiving unit. According to the CMOS image sensor, it is possible to have a structure which enables abutting a lens supporting member thereto easily in comparison with a CCD image sensor. However, it is desirable to consider a possibility of destruction of the CMOS image sensor by abutting a lens supporting member thereto carelessly.
In the CMOS image sensor according to the first aspect of the invention, because a first layer comprising a color filter array and a microlens array layered thereon, are provided on an upper surface of the light receiving unit; and a second layer comprising at least one of a color filter and a microlens array, is provided in a region of at least a portion of an upper surface of the signal processing circuit, the CMOS image sensor enables abutting a lens supporting member thereto through the second layer. As a result, it is not required to consider the adverse effect of variations in thickness of the adhesive between the substrate and the CMOS image sensor and the like, and further it is possible to reduce the possibility of destruction or malfunction, of the CMOS image sensor by abutting. Further, such a CMOS image sensor enables obtaining a miniaturized image pickup device.
Preferably, the signal processing circuit includes a digital signal processing circuit and the second layer is formed in a region of an upper surface of digital signal processing circuit.
In case that a color filter is disposed as the second layer, the color filter preferably comprises one of blue, red and green color filters.
The second layer preferably comprises a structure to enable placing a lens supporting member for supporting an optical lens, thereon.
The light receiving unit and the signal processing circuit is preferably formed in the same semiconductor chip, and the light receiving unit is formed in an approximate central region of the semiconductor chip and the signal processing circuit is formed in a peripheral region thereof.
The region in which the second layer is provided comprises at least separated three small regions which surround the light receiving unit.
Such a structure enables abutting a lens supporting member onto the upper surface of the CMOS image sensor, stably.
The second layer may be provided to cover almost whole upper surface of the digital signal processing circuit.